Correct incoming MQTT value

Add-ons Bindings
1

Hello everybody,

I have some temperature sensors which send their data via MQTT to my openhab server, this is the definition of one of these in the things-file:

  Thing topic sensor_01 "sensor 01" @ "room 39" {
    Type number : Temperature "Temperature" [ stateTopic="sensor_1/dht22/Temperature" ]
  }

Now I want to correct the incoming values (p.e. add 1) so that they are written with the corrected value in the persistence data, anyone who knows how to accomplish this?

2

Use incoming value transformation with JS to change the value in a channel level of as a profile to change it for individual items only

3

Hallo Matthias,

wäre dir um einen Tipp bzgl. der Anwendung der value transformation dankbar, habe das noch nie gebraucht und bin beim ersten Lesen jetzt nicht schlauer geworden :expressionless:

Hi Matthias,

thanks for your answer, I would be grateful for a tip on how to use the value transformation, I have never used it before and didn’t get any wiser after reading the documentation for the first time :expressionless:

4
  1. Install the js transformation add on
  2. Create a new js file in the transformation folder with your function
    E.g
(function(i) {
    return i*2;
})(input)
  1. Add the transformation to the channel (I only use UI based configuration, therefore not exactly sure about the syntax, but there are samples in the mqtt binding docu)
5

Hey, that’s great, thank you very much!!!

6

Ok, I tried the following now:

created a transformthevalue.js file in transform folder:

(function(i) {
    return parseFloat(i) - 10;
})(input)

Tested it with JavaScript Tester online, seems to work.

Changed the .items definition:
Number sensor_33_temperatur "Temperatur [%.1f °C]" <temperature> (gPersistence) { channel="mqtt:topic:mySecureBroker:sensor_33:Temperature" [profile="transform:JS", function="transformthevalue.js"], expire="30m,NULL"}

At first nothing happened, then I restarted openhab and now I get the following in the log file when the transformation should be executed:

[WARN ] [.thing.internal.CommunicationManager] - No ProfileFactory found which supports profile ‘transform:JS’

What did I miss? :confused:

7

My fault, installed JSONPath Transformation instead of JS Transformation :see_no_evil:
Now it’s working like a charm :slight_smile: